The present invention relates to a chuck for turning machines, and includes radially displaceably guided clamping jaws, each of which is adapted to be driven by a wedge bar that is disposed in the chuck body transverse to the longitudinal axis and is provided with teeth for engaging teeth of the clamping jaw. In addition, the wedge bars are displaceable in the chuck body beyond the clamping stroke to such an extent that the teeth thereof disengage from the pertaining clamping jaw and the latter can be removed radially from the chuck body. Each clamping jaw is provided with a locking mechanism that is respectively formed of an adjusting pin that is rotatably held in the chuck body and that by means of a cam, an eccentric, or the like engages in an angular recess formed in the wedge bar.
A chuck of this general type is known from DE-C 27 36 753. Although this known chuck has proved to be satisfactory in practice, if it is improperly handled the danger of an accident occurring cannot be precluded. In particular, in the case of internal clamping when the chuck rotates the clamping force is increased due to the centrifugal forces generated by the clamping jaws. If for an internal clamping a static clamping force that is too high is selected, and the increase clamping force due to rotation is not taken into account, it is possible under certain circumstances for cast pieces, such as thin-walled workpieces, to suddenly break. Due to the fact that the clamping force is reduced in an abrupt manner, the wedge bars are sometimes accelerated in such a way that the cams that are formed on the adjusting pins in an offset manner can be sheared off by the wedge bars. In such a case, the clamping jaws are no longer fixed in place so that there is a real danger of an accident when such a failure occurs.
It is therefore an object of the present invention to improve the locking mechanisms provided for a chuck of the aforementioned general type in such a way that even when breakage of a clamped-in workpiece occurs due to improper operation the locking mechanism prevents the teeth of the wedge bars and of the clamping jaws from disengaging so that these components cannot be hurled out. Rather, the wedge bars should always be fixed in place by the locking mechanism in such a way that they cannot be unintentionally shifted beyond their clamping stroke, so that they are reliably held by the locking mechanisms and accidents are thus precluded.